Similarity Of Urban Flora: Plants In Towns And Cities Are More Closely Related Than Those In The Countryside

October 2008 — More plant species grow in
German towns and cities than in the countryside, but those in towns and
cities are more closely related and are often functionally similar.
This makes urban ecosystems more susceptible to environmental impacts.

This is the finding of ecologists at the Helmholtz Centre for
Environmental Research (UFZ) who evaluated 14 million entries in the
German national FLORKART database, which has been built up by several
thousand volunteers over the past few years. They claim that because of
the altered environmental conditions, nature conservation needs to look
not only at conserving as many species as possible, but also at other
aspects of species diversity.

Writing in the October issue of Ecology Letters, the researchers say
that since urbanisation is already far advanced and will continue to
advance in future, we need to develop strategies to protect species
diversity even within towns and cities.

The urbanisation of the world is increasing rapidly. More than half
of the world’s population lives in towns and cities. In Europe the
figure is as high as 70 per cent. The fact that there is a higher
number of species in towns and cities than in the surrounding
countryside is due to a number of different reasons: many towns and
cities developed in geologically and structurally diverse landscapes,
so are naturally rich in species; the towns and cities themselves have
very diverse structures, temperatures are higher than in the
surrounding countryside, and alien species are often introduced into
towns and cities.

However, although towns and cities harbour more species than the
surrounding countryside, in terms of conserving biological diversity it
is not just the number of species that matters, but also their
relatedness (i.e. phylogenetic diversity). Every species is a carrier
of inherited information that determines e.g. pollination method and
leaf structure. The greater the phylogenetic diversity of a community,
the greater the probability that it will contain species with different
traits.

The traits and, consequently, the phylogenetic diversity, are
therefore the tools that enable plant communities to respond to
different environmental events. Without knowledge about traits and
relatedness (phylogenetics) our understanding of how communities
develop and how they deal with altered environmental conditions will
remain incomplete.

For their study, the researchers laid a grid of cells, each around
12 kilometres wide, over Germany and characterised the cells in terms
of land use. 59 cells were classified as urban landscape, 1365 as
agricultural and 312 as forest or near-natural landscapes. “Our
findings lead us to believe that different environmental filters
operate in urban areas and in rural areas,” explains Sonja Knapp of the
UFZ. The loss of phylogenetic information reduces a community’s ability
to respond to environmental changes and could in the long term have a
negative impact on the functions of urban ecosystems.